1. The Field of the Invention
The present invention relates generally to high speed telecommunications systems. More particularly, embodiments of the present invention relate to mechanisms for adjusting the rise and fall time in a laser transceiver while allowing for user configurability of the transition times even without the aid of an external controller.
2. Background and Relevant Art
Many high speed data transmission networks rely on optical transceivers and similar devices for facilitating transmission and reception of digital data embodied in the form of optical signals. Typically, data transmission in such networks is implemented by way of an optical transmitter, such as a laser, while data reception is generally implemented by way of an optical receiver, an example of which is a photodiode.
When employing a laser, the optical transmitter includes a laser driver. The laser driver controls the operations of the laser to properly convert electronic signals to optical signals for transmission over an optical network. The optical signal as transmitted is represented in digital form with a logical one often being represented by a higher optical intensity, and with a logical zero often being represented by a much lower optical intensity. In order to transmit a sequence of binary bits, it is often necessary for the optical signal to transition from the low optical intensity to the high optical intensity, and from a high optical intensity to a low optical intensity as appropriate given the information represented by the optical signal sequence.
The transition speed of the laser driver and the laser are greatly affected by temperature. Specifically, the transition speed tends to increase with colder temperatures. If the transition speed is too high, however, there can be several undesirable effects.
For example, if the optical signal transitions too quickly from high to low, the optical signal may undershoot the low optical intensity used to represent the logical zero (hereinafter also referred to as the “standard low optical intensity”). This increases the amount of time needed for the optical signal to settle to the standard low optical intensity. If the optical intensity undershoots too far, the laser may even turn off thereby significantly increasing the settling time. If the next transition from low to high is not within this settling time, the optical intensity may be above or below the standard low optical intensity. This means that next transition from low to high may occur sooner or later than desired. Accordingly, jitter is introduced into the optical signal sequence.
If the optical signal transitions too quickly from low to high, the optical signal may overshoot the high optical intensity used to represent the logical one (hereinafter also referred to as the “standard high optical intensity”). Once again, settling time is increased thereby introducing the potential for jitter.
The overshoot and undershoot problems discussed above may also have other undesirable effects. For example, before the electrical signal is converted into the optical signal, the overshoot and undershoot may causes electromagnetic interference to emit to the rest of the laser driver and telecommunications system, thereby potentially adversely affecting the performance of the telecommunications system as a whole.
Therefore, what would be advantageous are mechanisms in which the transition speed of the signal may be adjusted to reduce or eliminate overshooting and undershooting to thereby reduce jitter and electromagnetic interference. If would further be advantageous if this adjustment would permit a user to program the transition speed in response to empirical observations of the actual telecommunications system and depending on the sensitivity of the telecommunications system and network to jitter and electromagnetic interference. Furthermore, it would be advantageous if such a programmable transition time mechanism could be implemented without the use of an external controller thereby reducing the cost of the optical transceiver and associated telecommunications system.